The present invention relates to a prepaid or stored-value card with means for preventing useful fraudulent alteration.
It is known that prepaid cards of the magnetic type are already commercially available and are used for example for highway tolls, telephone services and so forth; their security is rather limited, since the card can be altered easily by anyone who has the equipment required to read/write the card.
Other conventional cards, such as for example chip-cards, have a built-in microprocessor and their security is entrusted to a plurality of authentications of various kinds which are performed directly by the microprocessor by means of a specific program contained therein. Those chip-cards have a good security degree, but their limitation is their relatively high cost.
Chip-cards without a microprocessor, such as for example the Siemens SLC443 card, are also known. Those cards have a five-stage octal counter which cannot be reloaded after its first activation and entail considerable limitations for applications outside the domain of telephony, since they have a counter in which each operation entails deducting one unit at a time; accordingly, it is unacceptable to use it if large unit values must be deducted because the system is extremely slow.
Moreover, this type of card has an operating limitation because after an average of 20-30,000 operations the card is physically no longer usable.
Other known solutions provide transponders for remote reading which have a low-cost EEPROM memory whose content can be read and rewritten freely, optionally by using suitable passwords, such as for example the TIRIS MPT16 transponders by Texas Instruments. This technology, however, currently has the limitation that it is not possible to write data related to a consumption of units in a manner that cannot be altered.